The present invention relates to a columnar support for knock-down furniture and the like and particularly an expansion locking device to be used in supporting, for instance, a top plate of a disassemblable table, a shelf, a container or other disassemblable articles of furniture.
Locking devices for locking a plurality of radially outwardly directed arm or foot members to a vertical column are presently known.
The arm and/or foot members of known structures of one type are constructed so as to be made integral to each other with the connection of these members to the upper and/or lower end of the column being obtained by a screw or by means of bolts, screws or the like. This solution is inconvenient because the arm members as well as the foot members become heavy and thus difficult to handle. This causes difficulties in the assembly and disassembly operations, and may cause damage to the threaded portion of exposed bolts.
The arm and foot members of some structures according to a second type are constructed as independent bodies, which have to be fastened together to the one or the other end of a vertical column.
A solution to these problems has been proposed which employs a locking device, comprising clamping means arranged at the inner ends of the arm and foot members and which engages inside clamping seats provided at the ends of the column.
This solution requires that provision be made at the ends of the column which include as many clamping seats as is the number of the arm and foot members respectively. That causes a steep increase in the manufacturing cost. Additionally a very high dimensional accuracy between the cooperating clamping surfaces is required in order to prevent oscillations of the arm and foot members, which could produce the instability of the article of furniture and/or a non-perfect horizontal position of a table-top plate or a shelf or the like supported by the carrying structure.
According to a third solution the independent arm and foot members are connected to the respective end of a vertical column by means of an expansion locking device, acting from the inside on the inner sector-like ends of the arm and foot members. This device comprises at least a body adapted to uniformly enlarge itself in radial directions and which is made of an elastomeric material. The body is placed between two washers mounted on a threaded rod in such a manner that as the rod is caused to rotate, the washers are caused to approach to one another tightening the resilient body disposed therebetween. This causes the radial expansion of the body so that the same applies radial pressures on the sector-like elements along a zone placed inside the hollow end portions of the column. But such an elastomeric body, which is provided for ensuring the locking between the aforesaid parts, tends to lose its elasticity relatively quickly with consequent loss of locking action.